New Holland UCM 9158 – UCM: Pattern Select (ISO/H): Short to Ground

The electrical circuit responsible for the Pattern Select switch, which allows the operator to toggle the electro-hydraulic (EH) joysticks between ISO and H control patterns, has shorted to ground. The control module detects zero voltage or an unintended ground path, preventing the machine from safely verifying or switching the control pattern.

• L213
• L215
• L216
• L218
• L220
• L221
• L223
• L225
• L228
• L230
• L234
• C227
• C232
• C234
• C237
• C238
• C245
• SR130
• SR175
• SV185
• TR270

1. 1

   Inspect the ISO/H Pattern Select rocker switch on the cab control panel for physical damage, sticking, or moisture intrusion.

2. 2

   Perform a harness isolation test: disconnect the electrical connector at the back of the Pattern Select switch and use a multimeter to check for continuity to ground on the signal wire. If the short is still present, the harness is damaged; if it disappears, the switch is internally shorted.

3. 3

   Check the EH (Electro-Hydraulic) system fuses in the main fuse box to ensure the short hasn't blown the circuit protection.

1. 1

   Power Down

   Turn off the machine and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Access the Switch

   Remove the necessary interior trim/paneling to access the rear of the Pattern Select rocker switch.

3. 3

   Disconnect

   Unplug the wiring harness connector from the switch.

4. 4

   Repair the Fault

   If the harness is damaged, locate the chafed wire (commonly where the harness routes near the cab pivot points or behind the panel) and repair it using proper splicing techniques and heat shrink, or replace the affected harness section. If the switch is faulty, squeeze the retaining tabs on the rocker switch to pop it out of the panel and snap the new OEM replacement switch into place.

5. 5

   Reassemble

   Reconnect the wiring harness to the switch and reinstall the cab trim panels.

6. 6

   Restore Power & Calibrate

   Reconnect the negative battery cable. Turn the key to the ON position and clear the inactive fault codes.

7. 7

   System Test

   Press and hold the ISO - H pattern select switch to the desired pattern for a few seconds. An audible alarm should sound, and the text display should confirm the change of the control pattern. Press the OPERATE button to activate the hydraulic system and verify joystick function.